High blood cholesterol (or hypercholesterolemia) is when you have too much cholesterol in your blood. It can cause heart disease, vascular disease and stroke. Cholesterol is a fat-like substance that circulates in the blood. It is an essential part of all cells in the body and is made by the liver. Cholesterol also comes from the animal-based foods we eat.
Cholesterol always travels through the blood within a transport protein—either a low-density lipoprotein (LDL) that delivers it to cells or a high-density lipoprotein (HDL) that sweeps up excess cholesterol and carries it back to the liver for rapid removal. Some people refer to LDL as the “lousy” or "bad cholesterol" and HDL as the “healthy” or "good cholesterol." Having lots of transport proteins with "bad" LDL cholesterol in your bloodstream can cause build-up on the blood vessel walls. The gradual build-up of cholesterol—together with fat, fatty cells, and other substances—in artery walls is called atherosclerosis. As this plaque builds up, it narrows the vessels enough to block blood flow and cause angina (chest pain), blood clots, a heart attack or stroke. Triglycerides are another type of fat in the blood that can speed up atherosclerosis.